After being out much of Wednesday, Facebook began to come back to life early Thursday after midnight ET for many users.

The outage is one of the longest the massively popular social network has ever experienced in its 15 years.

Facebook and Instagram started having problems at around noon Eastern time, with issues popping up across Facebook proper, Facebook Messenger and Instagram around the world.

Some users of Facebook-owned WhatsApp reported having issues sending photos on the popular messaging app.

It was not immediately clear what caused Wednesday's issue. Some users reported seeing a message saying the site was down for "required maintenance," while others were able to get the social networks to briefly load before discovering that functionality was limited.

In a tweet at 3:03 p.m. ET Wednesday, the company reiterated that it is still working on a fix. Facebook also confirmed that the outage was not the result of any distributed denial of service, or DDoS, attack.

We're focused on working to resolve the issue as soon as possible, but can confirm that the issue is not related to a DDoS attack.

In November, Facebook went down for about half hour and the company said the outage was the result of a “routine test.”

Rob Leathern‏, Facebook director of product, tweeted Wednesday afternoon that officials were “also aware that people are experiencing issues with access to our ads interfaces, we'll share an update as soon as possible.”